Chinese officials have accused vessels from Vietnam of launching more than 1,400 ramming raids on its ships near a drilling rig in the South China Sea.
The foreign ministry
said in a statement the actions were illegal and called on Hanoi to stop "provocations".
China moved the drilling rig on 2 May, helping to spark anti-Chinese riots in Vietnam in which four people died.
Hanoi says the rig is within its waters and has called on China to stop its exploration in the area.
The South China Sea is host to overlapping territorial claims by a number of countries.
Beijing claims almost the entire sea, based on a mid-20th Century map with a line apparently delineating Chinese territory, and vague historical claims going back more than 1,000 years.
The drilling rig is near the Paracel Islands, a grouping claimed by both China and Vietnam.
Hanoi argued that the rig was inside its Exclusive Economic Zone (EEZ), usually defined as within 200 nautical miles of a country's coast.
However, in its most detailed defence of the rig manoeuvre so far, China's foreign ministry said the drilling operation fell "well within China's sovereignty and jurisdiction".
"The two locations of operation are 17 nautical miles from both the Zhongjian Island of China's Xisha Islands [Paracels] ... yet approximately 133 to 156 nautical miles away from the coast of the Vietnamese mainland," the statement said.
Reference: BBC NEWS